The present invention relates to an exposure apparatus used for a semiconductor manufacturing process, and a projection exposure apparatus that projects and transfers a reticle pattern onto a silicon wafer. The present invention is suitable for an extreme ultraviolet (“EUV”) exposure apparatus that uses EUV light as exposure light with a wavelength of about 13 to 14 nm and a mirror optical system for projection exposure in vacuum.
A prior art example will be described with reference to FIGS. 6 and 7. 101 uses a YAG solid laser etc., and serves as an excitation laser for exciting light-source material atoms into plasma for light emissions by irradiating a laser beam onto an emitting point of the light source, at which the light-source material is in a state of gas, liquid or atomized gas. 102 is a light-source emitting part that maintains an internal structure to be vacuum. Here, 102A is a light source A indicative of an actual emitting point of an exposure light source.
103 is a vacuum chamber for accommodating an exposure apparatus entirely, which can maintain the vacuum state using a vacuum pump 104. 105 is an exposure light introducing part for introducing exposure light from the light-source emitting part 102, which includes mirrors A (or 105A) to D (or 105D), and homogenizes and shapes the exposure light.
106 is a reticle stage, and a movable part of the reticle stage is mounted with a reflective original form 106A that forms a pattern to be exposed.
107 is a reduction projection mirror optical system that reduces and projects an exposure pattern reflected from the original form 106A through mirrors A (or 107A) to E (or 107E) sequentially at predefined reduction ratio.
108 is a position-controlled wafer stage for positioning a wafer 108A as a Si substrate onto a predetermined exposure position so that the wafer stage can be driven in six axes directions, i.e., driven in XYZ directions, tilt around the XY axes, and rotated around the Z axis. The pattern on the original form 106A is to be reflectively reduced and projected onto the wafer 108A.
109 is a reticle stage support for supporting the reticle stage 105 on the apparatus installation floor. 110 is a projection optical system body for supporting the reduction projection mirror optical system 107 on the apparatus installation floor. 111 is a wafer stage support for supporting the wafer stage 108 on the apparatus installation floor.
Provided between the reticle stage 105 and the reduction projection mirror optical system 107 and between the reduction projection mirror optical system 107 and the wafer stage 108, which are distinctly and independently supported by the reticle stage support 109, the projection optical system body 110 and the wafer stage support 111, are means (not shown) for measuring relative positions to continuously maintain a predetermined arrangement of them.
A mount (not shown) for violation isolation from the apparatus installation floor is provided on the reticle stage support 109, the projection system body 110, and the wafer stage 111.
112 is a reticle stocker as a storage container that temporarily stores, in an airtight condition, plural original forms 106A as reticles supplied from the outside of the apparatus and suitable for different exposure conditions and patterns. 113 is a reticle changer for selecting and feeding a reticle from the reticle stocker 112.
114 is a reticle alignment unit that includes a rotatable hand that is movable in the XYZ directions and rotatable around the Z axis. The reticle alignment unit 114 receives the original form 106A from the reticle changer 113, rotates it by 180°, and feeds it to the reticle alignment scope 115 provided at the end of the reticle stage 106 for fine movements of the original form 106A in the XYZ-axes rotating directions and alignment with respect to the alignment mark 115A provided on the reduction projection mirror optical system 107. The aligned original form 106A is chucked on the reticle stage 106.
116 is a wafer stocker as a storage container for temporarily storing plural wafers 108A from the outside to the inside of the apparatus. 117 is a wafer feed robot for selecting a wafer 108A to be exposed, from the wafer stocker 116, and feeds it to a wafer mechanical pre-alignment temperature controller 118 that roughly adjusts feeding of the wafer in the rotational direction and controls the wafer temperature within predetermined controlled temperature in the exposure apparatus.
119 is a wafer feed hand that feeds the wafer that has been aligned and temperature-controlled by the wafer mechanical pre-alignment temperature controller 118 to the wafer stage.
120 and 121 are gate valves that constitute a gate opening/closing mechanism for supplying the reticle and wafer from the outside of the apparatus. 122 is also a gate valve that uses a diaphragm to separate a space of the wafer mechanical pre-alignment temperature controller 118 from an exposure space, and opens and closes only when feeding in and out the wafer.
Such a separation using the diaphragm can minimize a capacity to be temporarily released to the air, and form a vacuum equilibrium state.
Thus, when the conventionally structured exposure apparatus supports and positions the mirrors A to E relative to the mirror barrel 107F as shown in FIG. 7, fine displacements and inclinations of the rotational axis in the in-plane translation shift direction occur, and the mirror deforms by its own weight. This cannot satisfy extremely strict mirror surface shape precisions below about 1 nm necessary for the projection optical system mirrors, the illumination optical system mirrors, and the light source mirrors.
When the mirror's surface precision and thus the optical aberration deteriorate, the projection optical system, in particular, deteriorates imaging performance to the wafer and lowers light intensity.
The exposure light introducing part introduces the exposure light from the light-source emitting part in such a conventionally structured exposure apparatus. The reduction projection mirror optical system reduces and projects the exposure pattern reflected from the original form illuminated by the mirrors A to D in the exposure light introducing part. The reduction projection mirror optical system makes a multilayer of Mo—Si on each of the mirrors A to E by vacuum evaporation or sputtering, and reflects the exposure light from the light source on each reflective surface. In this case, the reflectance per surface is about 70%; the rest is absorbed in the mirror base material and converted into heat. The temperature rises by about 10 to 20° C. in the exposure light reflecting area, and the reflective surface deforms by about 50 to 100 nm around the mirror peripheral even when the mirror uses a material having an extremely small coefficient of thermal expansion. As a result, extremely strict mirror surface shape precisions below about 1 nm necessary for the projection optical system mirrors, the illumination optical system mirrors, and the light source mirrors cannot be maintained. When the mirror surface precision, the projection optical system deteriorates imaging performance to the wafer and lowers light intensity.
In addition, the illumination optical system lowers the target light intensity, and causes non-uniform light intensity. The light source mirror deteriorates the light intensity, such as insufficient condensing. They result in deteriorated basic performance of the exposure apparatus, such as exposure precision and throughput.